There is a growing consensus that cross-ecosystem fluxes significantly influence the structure and stability of aquatic communities. What remains unclear, however, is the relative importance and potential interactions of those fluxes to/with other well-studied factors affecting aquatic community structure such as environmental parameters or regional-scale influences related to connectivity or habitat size. In this study we compare those different hypotheses by investigating their individual and combined influence on the functional structure of littoral benthic invertebrates’ communities in 9 northern Canadian lakes (total of 23 sites). In each site, we sampled in spring and summer for macro-invertebrates, we measured C,N, P content of both benthic litter and terrestrial leaves, and we recorded several standard local (pH, Dissolved oxygen, turbidity, conductivity, temperature) and regional -scale (area:perimeter ratio, lake connectivity) parameters. We then used a combination of model selection and ordination approaches to disentangle the relative importance of each main hypothesis and their interactions.
Results/Conclusions
When considered alone, models including only environmental or regional-scale variables performed best in explaining spatial variations in community structure. Although terrestrial subsidies contributed non-additively (indicating interactions) to combined models, our results suggest that environmental and regional parameters combined are the most important influence on aquatic community structure. However, some specific species or functional groups were strongly affected by subsidy quality. For instance, Chironomid’s abundances were closely correlated to subsidy C:N ratio, and shredders were affected by nitrogen proportion in subsidies, suggesting potential implications for ecosystem functioning. Overall, those results suggest that terrestrial subsidies have some effects on lake benthic communities, but that, at least under baseline conditions (in protected landscapes without steep human land-use gradients), those cross-ecosystem fluxes are not the dominant factors to understand spatial variations in lake communities. Closing knowledge gaps on cross-ecosystem subsidy effects is important to improve our understanding of how communities and functioning may change under human and/or climate driven changes in watersheds.
